During the past decade portable consumer electronic devices such as radios, mobile phones and pagers have become enormously popular with the general public. The small size and shape of these devices makes portability easy and very practical. However, because consumers carry these devices in a pocket or wear them on their clothing, the chances of the device being inadvertently hit, or dropped on the floor and damaged, is very high.
New circuit component packages such as ball grid array (BGA) components which are commonly found in portable electronic devices have proven to be much less tolerant to mechanical shock than the traditional Quad Flat Pack (QFP) technology. Most BGA packages have no stress relief built into their interposer that electrically and mechanically connects the Silicon die to the circuit board. When the circuit board is under tension or compression such as during mechanical shock, the result frequently is solder joint failure between the BGA package and the circuit board. Under mechanical shock such as when the circuit board and protective chassis are dropped or hit, the mechanics of the shock to the protective chassis transfer a great deal of stress to the PCB and thus to the circuit components physically located near the point of impact. It is the transfer of mechanical shock to the PCB that is primarily responsible for the BGA failure. This has forced some PCB manufacturers to undergo the expensive and time-consuming process of under-filling the BGA with a protective insulating material to reduce the amount of stress transferred to the BGA and minimize this inevitable mechanical shock.
Information relevant to attempts to address these problems can be found in portable electronic device manufacturing facilities around the world. However, the existing art suffers from lack of protection given to the circuit board and electronic components contained within the portable electronic device.
Referring to prior art FIG. 1, a portable electronic device 100 generally comprises a top chassis cover 1 and a bottom chassis cover 4 housing a circuit board 3 which is affixed to said bottom chassis cover at affixing points 5. Prior art FIG. 2. illustrates a cross-sectional view of the portable electronic device 100, taken along line A1xe2x80x94A2 comprising top chassis cover 1 and bottom chassis cover 4 housing a circuit board 3.
Although prior art FIG. 1 and FIG. 2 illustrate that circuit board 3 is affixed to bottom chassis cover 4, generally prior art includes circuit board 3 affixed to one of either top or bottom chassis cover or both chassis covers.
When a circuit board is affixed to the protective chassis on all ends with a screw or other affixing mechanism as illustrated in FIG. 1 and FIG. 2, the circuit board will bend with the mechanics, thus making the solder joints for micro BGA devices and other devices which are sensitive to mechanical stress susceptible to solder joint fracture. The closer a particular circuit component is to the protective chassis and circuit board affixing point, the greater the circuit component will be affected by the mechanical shock of the impact to that area on the protective chassis.
For the foregoing reasons, there is a need to protect the circuit board enclosed within a protective chassis from mechanical shock sustained from, for example, an impact with the ground or floor if a portable electronic device is dropped.
The invention provides a solution to the problem of damaged circuit components on a circuit board resulting from mechanical shock such as when a portable electronic device is hit or dropped. According to the invention, the circuit board is affixed substantially near the center of the long axis of the circuit board so that the ends of the circuit board along the longer axis can flex freely uninhibited by the chassis. In this case, according to the invention, since the circuit board is not rigidly attached to the chassis more of the mechanical shock will be absorbed by the chassis and not transferred to the circuit board. Using this method of affixing the circuit board to the protective chassis allows the mechanical shock to be transferred from the protective chassis to the approximate center of the circuit board where the circuit board is affixed to the protective chassis. Since the mechanical shock is transmitted substantially near the center of the circuit board, circuit components on the circuit board located away from the center of the circuit board will experience a reduced level of mechanical shock. This reduction in the level of mechanical shock increases the chances that the circuit components will not be damaged or become detached from the circuit board.